1. Field of the Invention
The present invention generally relates to a helicopter having a torque-correcting thruster device.
2. Description of the Prior Art
Helicopters have either one or two main lifting rotors. Controlling yaw is essential in preventing the helicopter from spinning out of control. In tandem rotor helicopters, those helicopters having two lifting rotors, both the propulsive force and those forces required for directional or yaw control are provided by the main rotors. An inherent aspect of controlling the yaw of the single rotor helicopter is the counteraction of the torque generated in driving the main rotor of the helicopter. This torque tends to rotate the entire aircraft in a direction opposite to the rotation of the main lifting rotor. This torque is generated by the resistance of the air to the driving of the rotor. The force required to counteract the torque is relatively large compared to the amount of force required to vary the attitude of the aircraft about its yaw axis. FIGS. 1A, 1B and 1C show a conventional single rotor helicopter 20. In this type of helicopter, the propulsive force is provided by main lifting rotor 22 and rotor blades 23 while yaw control has generally been provided by a second and smaller stabilizing rotor 24 located at the rear or tail 26 of boom 27. Rotor 24 rotates counter-clockwise as indicated by arrows 28. Stabilizing rotor 24 controls the yaw of helicopter 20. Rotor blades 23 overlap and rotate over a portion of boom 27. As shown in FIG. 1A, rotor blades 23 rotate counter-clockwise as indicated by arrows 29. The primary direction of flight of helicopter 20 is indicated by arrow 30. Stabilizing rotor 24 produces a sideways thrust indicated by arrow 32. Main lifting rotor 22 produces a downward thrust indicated by reference numeral 33. Sideways thrust 32 does not contribute to the forward thrust of the helicopter and is therefore wasted. A moment arm is defined by the distance D1 between stabilizing rotor 24, as measured from reference axis 36, and main rotor axis 38.
A conventional tandem rotor helicopter is shown in FIGS. 2A and 2B. Tandem rotor helicopter 40 has main rotor 42 that rotates blade 44 in one direction and a second main rotor 46 that rotates blade 48 in an opposite direction. The simultaneous operation of main rotors 42 and 46 substantially eliminates net torque effect. However, the tandem rotor configuration is relatively complex and expensive. Furthermore, tandem rotor helicopters are typically not as maneuverable as single rotor helicopters.
Another prior art technique to counteract the aforementioned torque has been to use two lifting rotors mounted on a common shaft wherein the rotors rotate in opposite directions. The torque generated each rotor counteracts the other rotor. By changing the torque of one rotor relative to the other, directional control is achieved. A further prior art manner in which directional control is accomplished has been to mount jets at the tail of the rotor craft. However, these prior art devices contribute significantly to the cost of the helicopter. Furthermore, the size of the helicopter must be increased in order to implement these prior art configurations for controlling yaw.
The prior art in Daggett, Jr. et al. U.S. Pat. No. 3,957,226 (“Daggett”) and Allongue U.S. Pat. No. 5,240,205 (“Allongue”) describe various apparatuses and devices to counteract torque. For example, Daggett describes ducted air flow that is directed aft and which flows downward through the center of the helicopter tail (identified as the aft portion). However, such ducted air flow does not provide counter torque. When the flow is directed to the side, such side-directed flow may provide a torque-correcting flow but does not contribute to the forward movement of the aircraft. Furthermore, the air flows are shared. This means that the more flow that is used to produce counter torque, less flow is available for use in forward thrust. Thus, if all the flow is used for counter-torque, then no flow will be available for forward thrust. Conversely, if all the flow is used for forward thrust, then no flow will be available for counter-torque. Allongue U.S. Pat. No. 5,240,205 describes a helicopter having a single mechanically-driven lift and propulsion rotor and a fuselage that is rearwardly elongate. The helicopter has an anti-torque system that comprises an auxiliary anti-torque rotor whose axis is substantially transverse relative to the elongate fuselage and which is disposed at the rear end of the fuselage to generate a first transverse force. This transverse force opposes the torque exerted on the fuselage by the lift and propulsion rotor of the helicopter. The anti-torque system includes a blowing anti-torque device that comprises at least one longitudinal slot formed in the side of the portion of the elongate fuselage that is subjected to the downdraft from the lift and propulsion rotor. The longitudinal slot is fed with fluid under pressure that it ejects downward in a manner that is at least approximately tangential to the portion of the fuselage to generate a second transverse force in the same direction as the first transverse force. The anti-torque system also has a vertical fin disposed at the rear end of the elongate fuselage. The vertical fin has a particular profile such that during forward flight, the vertical fin generates lateral lift in the same direction as the first and second transverse forces. However, the aforementioned blowing device is not used to directly counter the main rotor torque. Rather, the blower redirects some of the main-rotor downward flow (and forces) to a slightly lateral direction. The redirected main-rotor flow forces counteract the main-rotor torque. Stated another way, the force of the blowing device does not counter the torque of the main rotor and thrust, and does not impart an aft-directed thrust or force. Instead, the blowing device functions as a fluidic device that causes the rotor flow to move in a different direction rather than substantially straight down. A significant disadvantage of the anti-torque system of Allongue is the substantial cost in implementing such a system.
What is needed is a new and improved helicopter that addresses the issue of yaw control but which is relatively less complex than prior art helicopter configurations, and does not utilize wasteful side forces as a means of counteracting main rotor torque.